Drive mechanism for use in saws and the like



R. K. DAVIS v'mmh 2 1, 1967 DRIVE MECHANISM FOR USE IN SAWS AND THE LIKEFiled June 4, 1964 United States Patent fice airain Patented Mar. 21,1967 3,309,932 BREVE MECHANiSlil EGR USE IN SAWS AND THE Lm Robert K.Davis, St. Charles, Ill., assigner to Portabie Electric Tools, inc., acorporation of illinois Filed June 4, 1964, Ser. No. 372,558 7 Claims.(Cl. 74-44) This invention relates to power tools and in particular topower tools wherein the tool element is linearly reciprocated.

One conventional form of hand power tool comprises a saber saw whereinan elongated saw blade is carried at one end by a tool holder for linearreciprocation thereby to effect a desired sawing operation.Conventionally, the reciprocation of the tool holder is effected bymeans of an electric motor carried within a suitable housing of theapparatus and connected to the tool holder by means of a motionconverting mechanism arranged to convert the rotary drive of theelectric motor to the desired reciprocative drive of the tool holder.The present invention comprehends an improved mechanism for convertingthe rotary motion to the desired linear reciprocating motion.

Thus, a principal object of the present invention is the provision of anew and improved tool apparatus.

Another object of the invention is the provision of such a toolapparatus comprising new and improved means for converting rotary drivemotion to a linearly reciprocating motion of the tool holder.

Yet another object of the invention is the provision of such anapparatus wherein the mechanism is arranged to provide a greater speedof tool holder movement in one direction than in the opposite direction.

A further object of the invention is the provision of such an apparatuswherein the drive is selectively rotatable in opposite directions ofrotation and the mechanism is arranged to provide a greater speed ofmotion to the tool holder in one or the other of the directions ofreciprocation as a function of the direction of rotation of the drivemotor.

A further object of the invention is the provision of such apparatusincluding a tool holder, means for guiding the tool holder forreciprocal movement along a preselected path, a driver rotatable about afirst axis intersecting the path, a crank arm fixed to the driver, aconnecting link having first and second spaced portions, means pivotallyconnecting the first portion of the llink to the crank arm at apreselected distance from the first axis, and means connecting thesecond portion of the link to the tool holder for pivotal movement ofthe second portion about a second axis parallel to the first axis andspaced from the path of reciprocation of the tool holder,

the connecting means precluding relative movement be tween the secondportion and the tool holder in the direction of the path.

Still another object of the invention is the provision of such apparatuswherein the axis of pivoting of the first portion of the link on thecrank arm is spaced from the axis of pivoting of the second portion ofthe link relative to the tool holder a distance greater than twice thedistance of the axis of pivoting of the first portion of the link on thecrank arm from the axis of the driver.

Other objects and advantages of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingwherein:

FIGURE 1 is a fragmentary side elevation of a saber saw provided with adrive mechanism embodying the invention;

FIGURE 2 is a fragmentary vertical section thereof taken substantiallyalong the line 2-2 of FIGURE 1; and

FIGURE 3 is a fragmentary horizontal section taken substantially alongthe line 3 3 of FIGURE 2.

In the exemplary embodiment of the invention as disclosed in thedrawing, a power tool herein comprising for illustrative purposes asaber saw generally designated 10 is shown to include a housing 11provided with a manipulating handle portion 12. Carried on the housingis a conventional shoe device generally designated 13 arranged to slideover the work vwhich is to be cut by means of a saw blade 14 extendingdownwardly through a suitable slot 15 in the shoe device.

The operationtof the saw is eected by a conventional electric motor 16mounted within the housing 11 and energized through suitable wires 17connected to a cable 1S extending outwardly from the handle 12. Themotor includes a shaft 91 journalled in a bearing 20 and having anoutboard gear 21 formed integrally therewith. Gear 21 drives a largegear 22 fixed to a stub shaft 23 journa=lled in the housing 11 by meansof a pair of bearings 24 and 25 disposed at opposite sides of the gear22.

Thus, shaft 23 is rotated in response to the rotation of the motor shaft19. The present invention comprehends an improved mechanism generallydesignated 26 arranged to convert the rotary motion of shaft 23 to thedesired reciprocating motion of the saw blade 14. More specically,mechanism 26 includes a crank arm 27, a link 28, a tool holder slide 29,pivot means 30 connecting the crank arm to the link, pivot means 31connecting the link to the tool holder slide, and a securing device 32for securing the upper end of the blade 14 to the tool holder slide.

The crank arm 27 includes a center portion 33 fixed to the stub shaft 23for rotation with the stub shaft about the longitudinally axis thereof.A first end portion 34 of the crank arm comprises a counterweight havinga circular sector shape as best seen in FIGURE 2. The pivot means 30includes a pivot pin 35 fixed-ly secured to the opposite end portion 36of the crank arm 27 and eX- tending forwardly therefrom through abushing 37 fixed in the link 28. A steel washer 38 may be disposed aboutthe pin 3S between the crank arm 27 and connecting link 28, as shown inFIGURE 1, and the outer end 39 of the pin 35 may define a retaininghead. Thus, the pin 35 defines a pivotal axis spaced from the axis ofrotation of the stub shaft 23 a preselected distance and moving in acircular path about the axis of the stub shaft 23 as the crank arm 27 isrotated.

The bushing 37 is mounted in a first end portion 40 of the link 28,which end portion is circumferentially enlarged at 41 to dene asupplemental counterweight. A pivot pin 42 is fixed to the opposite endportion 43 of the connecting link 2S and projects forwardly therefrominto a roller bearing device 44 o f the pivot means 31. The rollerbearing device 44 is carried in a collar 45 fixedly secured to the toolholder slide 29 and having a forwardly projecting member 46 slidablyengaging a guide 47 carried on the housing 11 for maintaining therotational position of the tool holder slide 29 whereby the saw blade 14is maintained accurately in a single plane. The tool holder slide isslida'bly mounted in a pair of spaced bearings 48 and 49 carried on thehousing 11 for reciprocation by mechanism 26 so Ias to effect thedesired reciprocation of the saw blade 14 in a path defined by thestraight line axis of the tool holder slide.

As best seen in FIGURES 2 yand 3, the collar 45 includes an offsetportion 50 for receiving the bearing 44 and pin 42 with the axis of thepin spaced laterally of the vertical axis of the tool holder slide 29.In the illustrated embodiment, the displacement of the axis of pin 42from the axis of the tool holder slide is approximately .215 inch. Asbest seen in FIGURE 2, when the tool holder slide is at its lowerrnostextreme position, the link 28 is disposed at a small -angle to thevertical plane, and more specifically, the plane defined by the axis ofpin 42 and the axis of pin 35 is at an angle of approximately 9 to thevertical plane defined by the axis of the slide 29 and the axis of thestub shaft 23 which is perpendicular to and intersects the axis of theslide 29. As further shown in FIGURE 2, when the tool holder slide is inits extreme uppermost position, the link 28, as shown in dotted lines,is in an upper position wherein the link is inclined at a somewhatgreater angle to the vertical, and more specifically, the plane definedby the axes of the pin 42 and pin 35 is inclined at an angle ofapproximately 30 to the vertical plane defined by the axes of the slide29 and the stub shaft 23.

Thus, assuming that the direction of rotation of the motor 16 is such asto cause a clockwise rotation of the crank arm 27, as seen in FIGURE 2,there will be approximately 201 of movement of the crank arm during theupward movement of the tool holder slide 29 from its lowerrnost positionto its uppermost position. Resultingly, there will be a rotation of thecrank arm 27 of approximately 159 during the movement of the tool holderslide 29 from its uppermost position to its lowermost position. Thus, itmay be seen that the tool holder slide will move more slowly upwardlythan downwardly whereby a relatively slow cutting speed is obtained.However, by providing electric motor 16 as a reversing motor, suitablereverse rotation of the motor to effect a counterclockwise rotation ofthe crank arm 27, as seen in FIG- URE 2, will cause the 159 portion ofthe movement of the tool holder slide to correspond to the upwardmovement thereof and the 201 portion of the motion to correspond to thedownward movement thereof whereby a relatively high speed cuttingoperation is effected. It should be noted that in each case the returnspeed of the tool holder slide is complementary to the cutting speed,that is the same total amount of time for a complete reciprocation ofthe saw blade is provided with the cutting time being selectivelyincreased or decreased as a function of the direction of rotation of themotor 16.

As seen in FIGURE 2, in the illustrated arrangement of the mechanism 26,the pin reciprocates between a position to the left of the verticalplane of the axis of the tool holder slide 29 at the lowerrnost positionof the tool holder slide and to the right of this plane when the toolholder slide is in its uppermost position. Further, it should be notedthat the counterweight 41 is roughly 180 out of phase in its rotationalposition relative to the counterweight 34, thereby effectivelycounterbalancing the lateral vibrations introduced by the counterweight,34. Y

While I have shown and described one embodiment of my invention, it isto be understood that it is capable of many modifications. Changes,therefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

I claim:

1. Apparatus comprising: ra tool holder; means for guiding said toolholder for reciprocal movement along a preselected path; a driverrotatable selectively in opposite directions of rotation about a firstaxis intersecting said path; a crank arm fixed to said driver; aconnecting link having first and second spaced portions; means pivotallyconnecting said first portion of said link to the crank arm at apreselected distance kfrom said first axis; and means connecting saidsecond portion of said link to said tool holder for pivotal movement ofsaid second portion about a Second `'cutis parallel to said first axisand spaced from said path of reciprocation of said tool holder, saidconnecting means precluding relative movement between said secondportion and said tool holder in the direction of said path.

2. Apparatus comprising: a tool holder; means for guiding said toolholder for reciprocal movement along a preselected path; a driverrotatable about a first axis intersecting said path; a crank arm fixedto said driver; a connecting link having first and second spacedportions; means pivotally connecting said first portion of said link tothe crank arm at a preselected distance from said first axis; and meansconnecting said second portion of said link to said tool holder forpivotal movement of said second portion about a second axis parallel tosaid first axis and spaced from said path of reciprocation of said toolholder, said connecting means precluding relative movement between saidsecond portion and said tool holder in the direction of said path.

3. The -apparatus of claim 2 wherein said path comprises a straight lineand said first axis is perpendicular to said line.

4. Apparatus comprising: a tool holder; means for guiding said toolholder for reciprocal movement along -a preselected straight line in apreselected plane; a driver rotatable about a first axis in said plane;a crank arm fixed to said driver; a connecting link having first andsecond spaced portions; means pivotally connecting said first portion ofsaid link to the crank arm at a preselected distance from said firstaxis; and means connecting said second portion of said link to said toolholder for pivotal movement of said second portion |about a second axisparallel to said first axis and spaced from said plane and defining withsaid first axis a second plane intersecting said preselected plane at anangle of approximately 9 when the tool holder is at one extreme of itsreciprocal movement, said connecting means precluding relative movementbetween said second portion and said tool holder in the direction ofsaid line.

5. The apparatus of claim 4 wherein the axis of pivoting of said firstportion of the link relative to said crank arm defines with said firstaxis a third plane intersecting said preselected plane at an angle ofapproximately 30 from the opposite side of said preselected plane whenthe tool holder is at the opposite extreme of its reciprocal movement.

6. Apparatus comprising: ia tool holder; means for guiding said toolholder for reciprocal movement along a preselected line; -a driverrotatable about a first axis; a crank arm fixed to said driver andhaving a counterweight means spaced from said axis; a connecting linkhaving first and second spaced portions and second counterweight meansadjacent said first portion having less mass than the counterweightmeans of said crankA arm; means pivotally connecting said first portionof said link to the crank arm at a preselected distance from said firstaxis diametrically opposite said counterweight means of the crank arm;and means connecting said second portion of said link to said toolholder for pivotal movement of said second portion about a second axisparallel to said first axis and spaced from said line of reciprocationof said tool holder, said connecting means precluding relative movementbetween said second portion and said tool holder in the direction ofsaid line.

7. Apparatus comprising: a tool holder; means for guiding said toolholder for reciprocal movement along a preselected substantiallystraight line; a driver rotatable about a first axis; a crank arm fixedto said driver; a connecting link having first and second spacedportions; means pivotally connecting said first portion of said link tothe crank arm for pivotal movement of said first portion about a secondaxis spaced from said first axis; means connecting said second portionof said link to said tool holder for pivotal movement of said secondportion about a third axis parallel to said first axis, said connectingmeans precluding relative movement between said 5 6 second portion yandsaid tool holder in the direction of References Cited by the ExaminerSaid line, Said line eXeIldIlg at all angle t0 the plan defined by saidrst and third axes to provide a difference in the speed of the toolholder movement in one 1,138,892 5/ 1915 Roberts 74-44 direction of saidreciprocal movement from the Speed 5 1,279,462 9/1918 Slegel 74-44thereof in the .other direction; and means for rotating 2,350,334`6/1944 Baker 74-44 said driver selectively in opposite directions ofrotation 215731753 11/1951 Young et 31- 74-44 about said rst ,axiswhereby the greater Speed ,of move- 2,961,016 11/ 1960 Papworth 143-68ment of the tool holder is selectively said one direction or said otherdirection corresponding to the selected l01:REDC1VJ1A'1`F1`1'3R1`1,IR.,PnmaryExaminer, direction of rotation ofsaid driver. F. E. BAKER, Assistant Examiner.

1. APPARATUS COMPRISING: A TOOL HOLDER; MEANS FOR GUIDING SAID TOOLHOLDER FOR RECIPROCAL MOVEMENT ALONG A PRESELECTED PATH; A DRIVERROTATABLE SELECTIVELY IN OPPOSITE DIRECTIONS OF ROTATION ABOUT A FIRSTAXIS INTERSECTING SAID PATH; A CRANK ARM FIXED TO SAID DRIVER; ACONNECTING LINK HAVING FIRST AND SECOND SPACED PORTIONS; MEANS PIVOTALLYCONNECTING SAID FIRST PORTION OF SAID LINK TO THE CRANK ARM AT APRESELECTED DISTANCE FROM SAID FIRST AXIS; AND MEANS CONNECTING SAIDSECOND PORTION OF SAID LINK TO SAID TOOL HOLDER FOR PIVOTAL MOVEMENT OFSAID SECOND PORTION ABOUT A SECOND AXIS PARALLEL TO SAID FIRST AXIS ANDSPACED FROM SAID PATH OF RECIPROCATION OF SAID TOOL HOLDER, SAIDCONNECTING MEANS PRECLUDING RELATIVE MOVEMENT BETWEEN SAID SECONDPORTION AND SAID TOOL HOLDER IN THE DIRECTION OF SAID PATH.